Abstract: | Two experiments measured changes in binocular eye alignment from 1- to 6-month-old human infants. In Experiment 1 changes in binocular eye alignment were recorded from 1, 2, and 3 month olds using corneal photography. A luminous target was moved along the infant's midline at one of two constant speeds. Infants at all three ages showed some evidence of appropriate changes in binocular eye alignment (convergence as the target approached and divergence as the target receded). The likelihood of appropriate convergence and divergence increased with age, as did the ability to respond appropriately to the faster target motion. A measure of convergence lag (further decrease in interpupillary distance after target motion had ended) was obtained for trials on which the target approached the infant. Convergence lag decreased with age and was greater on trials at the faster target speed until 3 months of age. Experiment 2 measured the responses of 3, , and 6 month olds as a wedge prism was placed alternately in front of each eye. The prism displaced the image nasally (either 2.5° or 5°), creating inappropriate binocular eye alignment. A refixation eye movement in response to the prism was not present consistently until 6 months of age. Hypotheses as to the mechanism controlling infant binocular eye alignment are discussed with respect both to the present findings and to findings from human adults and animals. |